Lagoon Estuary Research Articles

The contribution of ENSO cycles to the salinity spatio-temporal variability in a bar-built microtidal estuary

Estuaries are highly dynamic, complex and one of the most productive ecosystems in the world. In the Patos Lagoon estuary, which is connected to the South Atlantic Ocean through a single inlet, the saltwater transport into and out of the estuary is intimately connected to the wind and river discharge from the main tributaries, as tidal effects are small and restricted to the lower region of the lagoon (estuary). However, little is known about the spatio-temporal variability of salinity within the lagoon itself, making it the focus of this study. Salinity variability was investigated over a five-year period (2002–2006)​ applying the TELEMAC-3D numerical model. After calibration and validation, model results were compared to river discharge and wind time series to identify correlations with salinity variations along the estuary. Wavelet analysis was applied to time series of salinity and indicated that river discharge influences salinity patterns at long time scales (> 128 days), while synoptic forcing modulates its variability at shorter timescales (< 15 days). Results also show that in years of higher river discharge and NE wind predominance (El Niño), salty waters are pumped out of the estuary. On the other hand, in years of lower river discharge and SW wind predominance (La Niña), salty waters are pumped into the estuary. Thus, on an interannual timescale, El Niño Southern Oscillation (ENSO) cycles influence salinity variability in Patos Lagoon, since it changes atmospheric conditions (winds and precipitation) and, consequently, river discharge.

Storm tide amplification and habitat changes due to urbanization of a lagoonal estuary

Abstract. In recent centuries, human activities have greatly modified the geomorphology of coastal regions. However, studies of historical and possible future changes in coastal flood extremes typically ignore the influence of geomorphic change. Here, we quantify the influence of 20th-century man-made changes to Jamaica Bay, New York City, on present-day storm tides. We develop and validate a hydrodynamic model for the 1870s based on detailed maps of bathymetry, seabed characteristics, topography, and tide observations for use alongside a present-day model. Predominantly through dredging, landfill, and inlet stabilization, the average water depth of the bay increased from 1.7 to 4.5 m, tidal surface area decreased from 92 to 72 km2, and the inlet minimum cross-sectional area expanded from 4800 to 8900 m2. Total (freshwater plus salt) marsh habitat area has declined from 61 to 15 km2 and intertidal unvegetated habitat area from 17 to 4.6 km2. A probabilistic flood hazard assessment with simulations of 144 storm events reveals that the landscape changes caused an increase of 0.28 m (12 %) in the 100-year storm tide, even larger than the influence of global sea level rise of about 0.23 m since the 1870s. Specific anthropogenic changes to estuary depth and area as well as inlet depth and width are shown through targeted modeling and dynamics-based considerations to be the most important drivers of increasing storm tides.

Age, growth, mortality, reproduction, and exploitation rates for fishery management of grey mullet species in the Köyceğiz Lagoon–Estuary (Mediterranean coast)

Age, growth, mortality, reproduction, and exploitation rates for fishery management of grey mullet species in the Köyceğiz Lagoon–Estuary (Mediterranean coast)

Selenium Enrichment in Pore Water of Estuarine Sediments Subject to Salt Marsh Vegetation Bioirrigation (Patos Estuary, Southern Brazil).

Selenium (Se), iron (Fe), and free sulfides contents in pore waters were measured to study the liberation of soluble Se in suboxic conditions. The sediment core was collected in a salt marsh in Patos Lagoon estuary (southern Brazil), and it was obtained during a brackish water period, in a low intertidal stand vegetated by Spartina alterniflora. The redox potential (Eh), pH, andacid volatile sulfides (AVS) content were also investigated. Pore water results sustained the idea that S. alterniflora roots promote oxygen penetration to depths of ca. 10cm below the salt marsh surface, increasing Eh and lowering the pH in this interval. High Se concentrations (e.g., 16.9µg L-1), that are above US. EPA environmental criteria, were observed in the pore water to depths between 10 and 20cm and are associated to low AVS contents and high concentrations of free sulfides. In the first 10cm the lowering of Se contents probably happens due the low pH and biological volatilization of the metalloid.

Where is the nursery for amphidromous nekton? Abundance and size comparisons of juvenile ayu among habitats and contexts

The use of estuarine and marine ecosystems by amphidromous fishes has not been thoroughly studied, especially with respect to habitat types. Here, abundance and size comparisons of juveniles of an amphidromous fish, ayu (Plecoglossus altivelis altivelis), were performed among four types of topographically distinct shallow, soft-bottom habitats across two different environmental contexts (marine and estuarine) through monthly seining along an estuary–ocean ecotone in southern Japan. Topography (open/enclosed and presence/absence of surf zone) and environmental parameters (water temperature and salinity) differed among the four habitats, i.e., riverine estuary, exposed beach, embayed beach, and lagoon estuary. The peak month of juvenile abundance also differed among habitats (riverine estuary in December, exposed beach in January, embayed beach and lagoon estuary in March), as did the mean standard length (riverine estuary < exposed beach < embayed beach < lagoon estuary), although the abundance at embayed beach was significantly greater than in the two estuaries, and almost all size classes of juveniles occurred at embayed beach. A likely explanation for these patterns is that juvenile ayu select coastal habitats as they develop swimming ability and that riverine estuary/exposed beach, embayed beach, and lagoon estuary function as a corridor, primary nursery, and possible foraging ground, respectively. These findings, coupled with implications from previous studies of habitat selection in coasts by anadromous fishes, highlight the importance of seascape-level analysis for elucidating the nursery functions of coastal habitats, even for diadromous nekton. Regional termsNorth-western Pacific, East Asia, Japan, Kyushu, Miyazaki Prefecture.

Fine-scale genetic structure in Lahille’s bottlenose dolphins (Tursiops truncatus gephyreus) is associated with social structure and feeding ecology

Varying levels of population structure may arise from interactions between intrinsic behavioral and demographic factors and extrinsic environmental factors. Social organization, habitat use, resource partitioning, or even individual preferences are putative drivers of population genetic differentiation over fine spatial scales. Here, genome-wide data from single-nucleotide polymorphisms (SNPs) and carbon and nitrogen stable isotope data were used to examine population structure and niche partitioning among three social units of bottlenose dolphins with strong home range overlap in a relatively small geographic area in southern Brazil. Results from model-based and model-free analyses of population structure supported the delineation of two populations, one with preferences for estuarine waters and another strictly coastal, consistent with isotopic niche differentiation. These findings suggest that genetic and ecological structuring is mainly driven by habitat use. At finer scale, we also detected low but significant genetic differentiation among the three social units. The outcomes of this study provide new insights into population structure of Lahille’s bottlenose dolphins in the Patos Lagoon estuary and its adjacent coastal waters, which are exposed to increasing levels of anthropogenic disturbances, such as intensive artisanal fisheries, pollution, and boat traffic. Although for demographic studies, the estuary and the coastal dolphins should be treated separately, for conservation purposes, we recommend that the three social units be regarded as different entities.

Hydrologic controls on CO2 chemistry and flux in subtropical lagoonal estuaries of the northwestern Gulf of Mexico

Estuaries are generally considered a source of CO2 to the atmosphere, although with significant uncertainties in magnitude and controlling factors between and within estuaries. We studied four northwestern Gulf of Mexico estuaries that experience extreme hydrologic conditions between April 2014 and February 2017 to determine the role of dry/wet cycle on estuarine CO2 system. Annual air–water CO2 flux ranged from 2.7 to 35.9 mol·C·m−2·yr−1; CO2 flux declined by approximately an order of magnitude along with declining river discharge. Episodic flooding made CO2 flux differ between dry (−0.7 to 20.9 mmol·C·m−2·d−1) and wet (11.6–170.0 mmol·C·m–2·d–1) conditions. During wet condition, increases in dissolved inorganic carbon (DIC) and total alkalinity (TA) significantly elevated CO2 degassing. Furthermore, ventilation of river‐borne CO2 strengthened degassing when estuaries became overwhelmingly river‐dominated. During flood relaxation, all estuaries experienced heightened productivity, evidenced by DIC and TA consumption in the mid‐salinity range (10–30). When prolonged drought led to hypersalinity (&gt;36.5), biogeochemical and evaporative effects enhanced DIC and TA consumption and CO2 degassing. Due to flooding and high wind speeds, these estuaries were a strong CO2 source during spring and summer. Then they transitioned to a weak CO2 source or sink during the fall. Low temperatures further depressed CO2 efflux during winter except when a pulse of freshwater input occurred. This study demonstrates that changes in the hydrologic condition of estuaries, such as dry/wet cycle and river discharge gradient, will greatly alter air–water CO2 flux and estuarine contribution to the global carbon budget.

The effects of Microcystis aeruginosa cells lysate containing microcystins on physiological and molecular responses in the nematode Caenorhabditis elegans.

Microcystins (MCs) are potent toxins produced by environmental cyanobacterial blooms. The present study evaluated the effects of a Microcystis aeruginosa cyanobacterial lysate containing 0.1, 1, and 10 μg L-1 MC-LR equivalent in the C. elegans Bristol N2 wild-type and the effects caused by equivalent concentrations of a MC-LR standard. The lysate was prepared from a culture of toxic strain (RST9501) originated from the Patos Lagoon Estuary (RS, Brazil). The minimal concentration necessary to cause significant effects in C. elegans under exposure to M. aeruginosa lysate or to MC-LR standard were, respectively, 10 and 0.1 μg L-1 MC-LR equivalent for growth and 10 and 1 μg L-1 MC-LR equivalent for fertility. Reproduction (ie, brood size) was only affected by the exposure to 10 μg L-1 MC-LR standard and was not affected by the lysate. The nematodes that were exposed to lysate containing 1 μg L-1 MC-LR equivalent or MC-LR were also analyzed for pharyngeal pumping and gene expression using RT-qPCR. The worms' rhythmic contractions of the pharynx were similarly affected by the lysate containing 1 μg L-1 of MC-LR equivalent and the MC-LR standard. The MC-LR standard caused down-regulation of genes related to growth (daf-16), fertility (spe-10), and biotransformation (gst-2). This is the first study to evaluate the effects of a toxic cyanobacterial lysate using the C. elegans model. This study suggests the organism as a potential biotest to evaluate toxicity of natural waters containing M. aeruginosa cells and to environmental risk assessment associated to cyanobacterial bloom events.

First detection of the non-indigenous gastropod Rapana venosa in the southernmost coast of Brazil

The rapa whelk Rapana venosa is a predator of bivalves, native to Eastern Asia. It was first recorded outside its native distribution in 1946 in the Black Sea and since then has invaded estuarine and marine waters worldwide. The present findings increase the known geographic distribution of reproducing populations to eight regions: Black, Adriatic and Aegean seas, the coast of Brittany, the coast of the Netherlands, Chesapeake Bay, La Plata River estuary in Argentina-Uruguay and the southern Brazilian coast. We present the first records of R. venosa in the southernmost Brazilian coast (between Hermenegildo and Cassino Beaches, RS), based on 110 specimens, one as an epibiont associated with the green sea turtle Chelonia mydas. The majority of the specimens were found along Cassino beach, close to the inlet of the Patos Lagoon estuary (~32°S). Despite the highly variable salinity in the estuarine area, R. venosa was able to invade this area, probably due to its high fecundity and fertility, fast growth rate and high tolerance to salinity and temperature variations, all characteristics of a successful invader. The presence of this species further to the north (about 800 km) of the La Plata River estuary shows that it is dispersing along the southwestern Atlantic. Its interaction with green turtles may be of global importance for sea turtle conservation, given the observed potential for dispersal using turtle carapaces, which may affect their swimming and feeding. Our study contributes to the knowledge of bioinvasion in the Southwestern Atlantic coast.

Sulfate reduction and alterability of sulfur species in sediments of an estuary with irregular hydrological regime

The irregular hydrological regime in Patos Lagoon estuary has been suggested as having a distinctive influence on sulfur speciation in sediments. We performed an investigation for different prolonged hydrological conditions focusing on the distribution of sulfides (acid volatile sulfide (AVS), chromium reducible sulfide (CRS), and Free-S2-) in sediment cores from salt marsh and non-vegetated shallow zone. Significant differences in sulfides content and distribution between the different hydrological periods were found. The predominance of more reducing conditions was observed during the freshwater period. It reflects a higher total reducible inorganic sulfur (TRIS) content in this period, with a great accumulation of AVS in sediments (> 100 mg kg-1). In the maximum salinity period, more oxidizing conditions prevailed, which significantly decreased the concentrations of metastable sulfides. The intense bioirrigation process exerts control over sulfide formation and distribution, which is as important as that exerted by the variations of the hydrological regime.

Habitat use in different life and moulting stages of Callinectes sapidus (Decapoda, Portunidae) in South Brazilian estuarine and marine environments

AbstractThe blue crab Callinectes sapidus is an important ecological and commercial species. It plays a fundamental role in the structure and function of coastal benthic food webs, with global catches of ~74,357 tons. This is the most exploited portunid species in Brazil. However, few studies about the ecology and population dynamics of C. sapidus have been published. This study aimed to analyse the preferred areas for the spatial distribution of juveniles and moulting individuals of C. sapidus in shallow areas of the Patos Lagoon estuary and the adjacent marine reproductive area, and their relation to water and sediment characteristics. Juveniles and moulting individuals preferred the embayment of the upper estuary, where the sediments are finer, with higher contents of organic matter and the presence of submerged vegetation. There was also a temporal variability in the abundance of juvenile size classes, with two marked increments of smaller individuals: (1) in late spring and summer and (2) in winter, indicating two recruitment peaks. Unusual environmental conditions in the summer of the first year, with an increase of fine sediments and organic matter, combined with low salinities in the adjacent marine area, allowed recruitment of individuals there. We suggest better attention to the embayment around the Marinheiros Island (considered here as upper estuary) for management and protection measures due to the overlapping of recruitment preferences of the blue crab, pink shrimp and fish species in this area.

The biggest or the most abundant? Predation of the Black Drum Pogonias cromis (Perciformes, Sciaenidae) on benthic organisms in southern Brazil

Predators that consume larger prey acquire a greater net return of energy per individual, even though they are less abundant. The objective of this work is to analyze the feeding biology of Pogonias cromis in southern Brazil, in order to test for the occurrence of ontogenetic changes in diet as fish reach larger sizes, by consuming larger prey as they grow. Between August 2014 and May 2016, 347 specimens were collected from catches of the fishing fleet that operate in the Patos lagoon estuary and in the adjacent marine area of Cassino beach, that use artisanal fishing gillnets. The prey-specific relative importance index, food overlap, niche breadth and prey length preference were calculated for three length classes, class 1 (27.8–48.73 cm), class 2 (48.73–69.66 cm) and class 3 (69.66–90.60 cm). A total of 13 food items (6 species of crustaceans, 5 species of mollusks, fish fragments and non-animal fragments) were identified, where two species of mollusks (Heleobia australis and Erodona mactroides) represented 90.49% of the diet. The overlap index was moderate between classes 1 and 2, high between 2 and 3 and moderate between 1 and 3. There was a low niche breadth at the population level and for each length class. There were no significant differences in the length of prey consumed among classes. The data obtained here indicates that P. cromis can be classified as a predator specialized in mollusks, with low tendency to ontogenetic changes in southern Brazil. Considering information from the population of P. cromis from Argentina, it can be inferred that the species in the waters of southern South America is a benthic predator adapted to local conditions.

Long‐term changes in fishery resources of an estuary in southwestern Atlantic according to local ecological knowledge

AbstractLong‐term changes in the abundance of fisheries resources from the Patos Lagoon estuary and adjacent coastal waters in southern Brazil have been observed. Despite this understanding, it is well known that the perception of pristine state of the environment is susceptible to inter‐generational changes, commonly known as shifting baseline syndrome (SBS). An useful approach in the reconstruction of pristine scenarios and in lack of data, as often occurs in small‐scale fisheries, is the local ecological knowledge (LEK). Temporal changes in the perception of 81 fishers with 1–63 years of fishing about the resources status were analysed. More experienced fishers reported larger catches, heavier individuals and perceived a greater number of species as "scarce" nowadays and "common" at the beginning of their careers proving the existence of a SBS among them. Over time, the number of fishing sites with very high catches decreased and fishing sites shifted from the lower towards the upper estuary. The perception of the fishers corroborated the real decreasing scenario in estuarine fisheries resources shared with industrial fishing in coastal waters. The results reinforce the utility of LEK for reconstruction of biological scenarios when no empirically obtained data are available.

Importance of Sample Gear in the Identification of Trophic Guilds and Forage Species in a Large Lagoonal Estuary

AbstractFood habits in Pamlico Sound, North Carolina, are poorly described despite the estuary's large size and importance as nursery and fisheries habitat. We conducted the first multi‐year, multispecies food habits study in Pamlico Sound, sampling the stomach contents of 16,913 predators representing 25 species. Predators were sampled from fisheries‐independent trawl and gill‐net surveys. We used multivariate analyses to compare diets between surveys, used agglomerative hierarchical cluster analyses and similarity profiles to identify significant trophic guilds, and identified forage fish using multiple approaches (qualitative classification criteria, connectance, and supportive role to fishery ecosystems [SURF]). The diets of predators sampled from the trawl survey were significantly different than predators sampled from the gill‐net survey. Mysids and anchovies were more important for trawl‐caught predators, with the majority of those predators belonging to nonpiscivorous guilds. Half of the gill‐net survey predators were piscivorous and relied more heavily on Atlantic Menhaden Brevoortia tyrannus and sciaenids. Differences in the level of piscivory between the surveys are most likely a result of larger predators being sampled in gill nets relative to trawls. There was little agreement among approaches in forage species identification, and only anchovies in the trawl survey were identified as a forage species using all approaches. Quantitative metrics identified forage species (e.g., Spot Leiostomus xanthurus and invertebrates) that were not identified by qualitative classification criteria. Our work shows the effect of gear size selection on estimates of predator diets and the need to use a variety of gears that sample a wide range of predator sizes. Additionally, the identification of forage species requires an evaluation of criteria outside of life history characteristics and a greater emphasis on the contribution of a prey species to a predator's diet.

Trophic Indicators of Ecological Resilience in a Tidal Lagoon Estuary Following Wastewater Diversion and Earthquake Disturbance

Estuary ecological resilience can be gauged by response of estuary trophic state to abatement of nutrient pollution. Changes in trophic indicators were studied in the Avon-Heathcote Estuary (AHE) in Christchurch, New Zealand, over 6 years, spanning diversion of city wastewater inputs to an offshore outfall in 2010, and to temporary enrichment caused by the 2011 Christchurch earthquake. It was hypothesised that the tidally well-flushed and sandy AHE would not harbour a ‘legacy’ of eutrophication and would rapidly gain improved ecological function following the diversion. AHE sediments were coarse (156 μm median grain size) with low organic matter (OM 1.2%, N 0.03%, C 0.3%), which changed little either with diversion or earthquake. Upon diversion, median water column and porewater ammonium (36, 185 μmol) decreased by 87% and 57%, respectively, benthic microalgae (269 mg chlorophyll-a m−2) fell by 58%, and enrichment-affiliated polychaetes (3700–8000 m−2) fell by 60–80% at sites with largest benthic microalgal reductions, all within < 1–2 years. Oxygen and ammonium fluxes were usually oligotrophic and changed little upon diversion, except near the historic wastewater discharge site. Denitrification became more important for N loss, increasing from 5 to 29% of estuary N load. Responses to earthquake-driven enrichment were transient. Despite decades of heavy N loading and eutrophic growths of benthic microalgae and macroalgae, the AHE did not store a eutrophic legacy in its sediments. It reacted rapidly to improved water quality allowed by the outfall, showing that this common estuary type (sandy, well-flushed tidal lagoon) was resilient to eutrophication upon stressor removal.

Interannual variation of bycatch assemblages of artisanal bottom shrimp-trawling on the Patos Lagoon estuary, Brazil

One of the most concerning problems of trawl fisheries today is the bycatch, especially given that over the last decade the Ecological Approach to Fisheries (EAF) has increased in importance. Bycatch variation is an important issue in fisheries management, since non-representative assessments of this topic can lead to the implementation of inadequate legislation. The assemblages of bycatch species in shrimp trawlings on the Patos Lagoon estuary and their relation to salinity, the size of the main species captured, and the bycatch to shrimp ratio were studied. Samples were taken between January 2011 and May 2014, encompassing four fishing seasons. We analyzed a total of 173 trawls, containing a joint total of 32,835 individuals. Sixty-one different types of bycatch species were captured, which were mostly (>80%) juveniles/non-mature individuals of commercial species. Eleven species dominated the captures, the most abundant of which were Micropogonias furnieri (FO > 82%), Callinectes sapidus (FO > 90%) and Genidens barbus (FO between 1.30–66.7%). There was a shift in assemblage structure according to salinity, which was reflected in the presence or absence of the lesser abundant species, but also in shifts on the density of the dominant species. Temperature was similar throughout the studied fishing seasons (23.9 ±3.3∘C), but salinity varied between 8.6 and 21.9. The bycatch to shrimp ratio was very high during the studied period (2011 = 3.3:1; 2012 = 2.6:1; 2013 = 8.7:1; 2014 = 65:1), but highest values were recorded when salinity was lower. However, even when environmental conditions favored pink shrimp abundance (high salinity), the ecological impact of this fishery was high, confirmed by the higher richness of species in the samples. Results call for a better fisheries management and supervision of illegal trawls.

Impacts of dredging on the hydromorphodynamics of the Patos Lagoon estuary, southern Brazil

Many estuaries present natural harbor conditions with relatively calm and shallow waters that provide a connection between the ocean and continental waterways. The increase in the demand for goods by the constant growing of the world population has forced estuaries to be altered by human activities, such as dredging, in order to maintain a safe navigation system. The development of sophisticated morphological and hydrodynamic models opened a new perspective of assisting dredging operations inside different estuaries. Thus, the aim of this study is to apply a hydromorphodynamic model to simulate the bed evolution of the Patos Lagoon estuary, southern Brazil. The results of the simulation were applied in a dredge operation model to simulate dredging inside the waterway of the Rio Grande harbor, located inside the Patos Lagoon estuary. The salinity and current velocities inside the estuary were well represented by the model simulations. An annual mean discharge of 3 407 ms3 s−1 was calculated for the lagoon for the year 2004. The morphodynamic model successfully represented the silted and eroded scenarios for the estuarine channel. The dredge operation model results affirm that dredging of the channel causes significant variations in estuarine physical parameters such as salinity, current velocity and suspended sediment concentration. The bed evolution results indicate that a fast siltation of the channel occurs right after dredging stops, stabilizing the variations after a 60-day period.

Surface coatings select their micro and macrofouling communities differently on steel

Previous studies have shown the effect of surface coatings on biofouling; however, they did not take into account the interaction of the micro and macrofouling communities, the effect of substrate orientation and the zooplankton-zoobenthic coupling together. Therefore, the aim of this study was to evaluate the effect of Zn- and Cu2O-based coatings on micro and macrofouling on steel surfaces, while also observing the role of substrate orientation and zooplankton supply. An experiment was carried out in the Patos Lagoon Estuary in southern Brazil for three months between spring and summer, where ASTM-36 steel plates represented different coatings (Zn- and/or Cu2O-based) and orientations (vertical and horizontal). To assess the zooplankton supply, sampling was carried out weekly using a 200 μm plankton net. Zn-based coating positively affected microfouling density compared to uncoated surfaces. The same pattern was observed with macrofouling, associated with vagile fauna preference, which represented 70% of the settled macrofoulers. Cu2O-based antifouling painted surfaces showed the highest microfouling density inhibition, while Zn + Cu2O-based coating did not affect the bacteria adhesion but showed lower density compared to Zn-based coating alone. The coatings combination showed the highest invertebrate inhibition. In this way, the macrofouling community was more sensitive than microfouling was to the antifouling coatings tested. The substrate orientation only affected macrofouling, horizontal surfaces being more attractive than vertical. Meroplankton, tychoplankton and holoplankton were recorded on the surfaces, although their representation in plankton was not proportional to the recruits recorded on the substrates. This was probably due to fast dispersion, the interactions of other factors and/or ecological succession stage. Surface coating, substrate orientation, and zooplankton supply interacted with the biofouling process on steel in different ways depending on the organism evaluated. Therefore, copper oxide- and zinc-based coatings were not suitable as coatings to avoid the total biofouling establishment.

Innovative Approaches for Geometric Uncertainty Quantification in an Operational Oil Spill Modeling System

Reliable and rapid real-time prediction of likely oil transport paths is critical for decision-making from emergency response managers and timely clean-up after a spill. As high-resolution hydrodynamic models are slow, operational oil spill systems generally rely on relatively coarse-grid models to provide quick estimates of the near-future surface-water velocities and oil transport paths. However, the coarse grid resolution introduces model structural errors, which have been called “geometric uncertainty”. Presently, emergency response managers do not have readily-available methods for estimating how geometric uncertainty might affect predictions. This research develops new methods to quantify geometric uncertainty using fine- and coarse-grid models within a lagoonal estuary along the coast of the northern Gulf of Mexico. Using measures of geometric uncertainty, we propose and test a new data-driven uncertainty model along with a multi-model integration approach to quantify this uncertainty in an operational context. The data-driven uncertainty model is developed from a machine learning algorithm that provides a priori assessment of the prediction’s confidence degree. The multi-model integration generates ensemble predictions through comparison with limited fine-grid predictions. The two approaches provide explicit information on the expected scale of modeling errors induced by geometric uncertainty in a manner suitable for operational modeling.

Modelling the spatio-temporal bycatch dynamics in an estuarine small-scale shrimp trawl fishery

The Patos Lagoon estuary in Southern Brazil is an important nursery ground for many commercially important fish and invertebrate species, with shrimp fisheries sustaining most of the surrounding small-scale fishermen. Although they are illegal, trawl gears are widely used by small-scale fishermen in order to catch shrimp. Shrimp trawl fisheries in tropical waters have high bycatch rates and cause a variety of problems, spanning from conflicts with other fisheries to changes in ecosystem trophic dynamics. A better understanding of the factors driving the bycatch process is therefore needed to establish reliable management measures. Here we used hierarchical Bayesian spatio-temporal models (HBSMs) to describe the bycatch of a small-scale shrimp trawl fishery in the Patos Lagoon estuary relative to a set of environmental and spatio-temporal predictors. Two different models were used to estimate bycatch trends: an effort-based method (BPUE) and a ratio-based method (BR, bycatch rate). A third model was used to evaluate the dynamics of shrimp catch per unit of effort (CPUE) as this measure is equally important to describe the underlying bycatch process. Overall, the bycatch consisted of 61 species of which 45 have market value. The mean bycatch rate was 86.2% for the entire period, which represents 6 kg of bycatch for every 1 kg of shrimp caught. Although the contribution of environmental variables differed among the models, the yearly spatial effect was identified as a common that explained bycatch dynamics. Moreover, the predictive maps revealed consistent hot and cold-spots from year-to-year, which varied in intensity for BR, BPUE and CPUE, and, therefore, represent a valuable benchmark for stakeholders and managers.